The present invention relates to a mechanical hook fastening element comprising a multiplicity of flexible hook elements emanating from a backing layer and comprising stems terminating in hook heads, said fastening element being releasably engagable with a complementary mechanical fastening element, the top portions of at least some hook heads and/or at least part of the interstitial spaces between the stems of said fastening means being covered with a pressure-sensitive adhesive. The invention also refers to a method of preparing said fastening element and to its use in absorbent articles such as disposable diapers.
Hook-and-loop fastening systems comprising a hook fastening element and a loop fastening element are widely used for a vast array of products and applications. More specifically, hook-and-loop fastening systems can be used for releasably closing garments, for example, disposable garments such as diapers or hospital gowns. There is a wide variety of methods of forming hook fastening elements for use in hook-and-loop fastening systems. Depending on the geometrical form of the hook and/or loop elements, the hook elements have different engagement mechanisms and characteristics with mating loop materials.
The hook fastening element described in U.S. Pat. No. 3,718,725 is made from a fabric having an orderly array of upstanding loops. After inserting rods into rows of loops to maintain their upstanding position, platens or rollers apply heat and pressure to melt each loop and its summit and to press each free molten end to form a knob or head that can interengage with the loop element of a hook-and-loop fastening system. Because the knobs or heads afford a mushroom appearance, this type of hook fastening is called xe2x80x9cmushroom-typexe2x80x9d. Mushroom-type hook fastening elements are also described, for example, in WO 94/23,610 and U.S. Pat. No. 5,077,970.
J-shaped hook fastening elements are described, for example, in U.S. Pat. No. 3,594,965, U.S. Pat. No. 4,994,339 and U.S. Pat. No. 5,315,740. The hook elements have a profile defined by an inner smooth contoured, generally concave face and a generally convex shaped outer face. The hook described in these patents tapers smoothly and continuously in width from the hook base to the hook free end. The hook element is allegedly designed so that it will not deform to release a loop engaged with the hook in shear mode or at a desired applied force.
A wide variety of sizes and shapes of hook elements are described in WO 94/23,610, WO 92/04,839 and U.S. Ser. No. 08/723,632 filed by the present applicant. Using methods described in these patent applications, a backing having a large number of upstanding thermoplastic stems is fed through a gap between a nip formed by, for example, two calendar rolls. The upper nip is smooth and heated so that the distal ends or tips of the stems are deformed under heat and mechanical pressure, forming various types of cap structures depending on the nip conditions selected, the relative speed of the stems in the nip, and the size and shape of the stems. The undeformed stem portion and the deformed cap together form a hook element.
U.S. Pat. No. 4,894,060 describes a hook fastening element comprising a thin strong flexible plate like backing, and a multiplicity of resiliently flexible spaced hook elements projecting at an essentially night angle from the upper surface of the backing. The hook elements each comprise a stem portion attached at one end of the backing, and a head portion at the end of the stem stem portion opposite the backing. The head portion projects past the stem portion on at least one of two opposite sides, and has a rounded surface opposite the stem portion to help the head portion enter between loops in a loop fastener element. U.S. Pat. No. 4,984,060 describes J- and T-shaped hooks as well as more complicated geometrical forms. J-shaped hook fastening elements are also described in U.S. Pat. No. 4,794,028 and U.S. Pat. No. 5,620,769.
Although a hook fastening element is typically sold with a complementary loop fastening element, the hook fastening element can also be used by itself to become releasably fastened to fabrics that can be easily penetrated by the hook elements. Mushroom-type and/orxe2x80x94appropriately sized hook fastening elements can, for example, be described to become releasably fastened to burlap, terry cloth and tricot. Mushroom-type hook fastening elements can also be designed so that two hook fastening elements can be used to fasten two articles together by adhering each hook fastening element to one of the articles and then interengaging the two fastening elements. Interengagable mushroom-type hook fastening elements are described, for example, in U.S. Pat. No. 3,192,589 or U.S. Pat. No. 4,290,174.
Mechanical hook-and-loop fastening systems have been proposed for use in disposable garment closure systems such as, for example, diapers and hospital gowns because the hook-and-loop system is unaffected by contaminations with, for example, talcum powder or baby oil which may destroy the holding power of pressure-sensitive adhesive closure systems. Mechanical hook-and-loop fastening systems, however, do not provide a disposal mechanism by which the soiled absorbent article may be folded or rolled up after use into a configuration for disposal, secured in the disposal configuration and conveniently thrown away. EP 0,321,232 therefore suggests closure tabs for disposable absorbent articles, particularly diapers, comprising a mechanical hook fastening element and additionally an adhesive fastening element on a second area of the closure tab of the closure system. While the mechanical hook fastening element is engagable with a complementary mechanical loop fastening element on the landing zone of the diaper and thus secures the diaper to the wearer""s body during use, the adhesive fastening element can adhere to the outside surface of the diaper when it is rolled up for disposal. Due to the additional adhesive securement means, the closure tab exhibits. however, an extended length which is not fully satisfactory from a design and cost point of view. EP 0,321,234 suggests to attach a third mechanical closure system to the body portion of the absorbent article which is engagable with the mechanical hook fastening element on the closure tab, thus providing a disposal means. Other solutions are disclosed, for example, in EP 0,529,681 including closure tabs comprising a hook fastening tab and an additional adhesive fastening element which could be, e.g. subjacent to the hook element on the fastening element or a separate adhesive fastening tab. The constructions of EP 0,321,234 and EP 0,529,691 are, however, relatively complicated and typically require explanation to the user.
It was therefore an object of the present invention to provide a mechanical hook fastening element offering in addition to the mechanical fastening mechanism an adhesive fastening mechanism to increase the versatility of said mechanical hook fastening element, It was another object of the present invention to provide a hook and loop mechanical closure system for disposable garments having a disposability feature. Other objects of the present invention can easily be taken by the person skilled in the art from the following detailed specification.
The present invention relates to a mechanical fastening element comprising a multiplicity of flexible hook elements emanating from a backing layer 1 and comprising stems 2 terminating in hook heads 3, said fastening element being releasable engagable with a complementary mechanical fastening element. Top portions of at least some hook heads and/or at least part of the interstitial spaces 4 between the stems 2 of said fastening element being coated with a hot-melt pressure-sensitive adhesive 5 so that the level of the adhesive in the interstitial spaces 4, where present, does not exceed the length of the stems 2. Also essentially no adhesive bridges are present between adjacent hook heads 3. The hot-melt pressure sensitive adhesive has a viscosity as measured at the coating temperature of between 2,000 and 18,000 mPa-s.
The present invention furthermore relates to a method of manufacturing a mechanical fastening element according to the invention, said method comprising passing a continuous sheet 7 of a mechanical fastening element comprising a multiplicity of flexible hook elements emanating from a backing layer 1 and comprising stems 2 terminating in hook heads 3, by a coating head 6 with the hook heads 3 facing the coating head 6, applying a hot-melt pressure sensitive adhesive having a viscosity as measured at the coating temperature of between 2,000 and 18,000 mPa-s, to the continuous sheet 7 by means of the coating head 6, orienting the coating head 6 with respect to the continuous sheet 7 of the mechanical fastening element so that the hot-melt pressure sensitive adhesive is coated onto at least part of the hook heads 3 and/or at least into part of the interstitial room 4 between the stems 2 of said fastening means so that the level of the adhesive in the interstitial rooms 4 where present does not exceed the length of the stems 2 and essentially no adhesive bridges are present between the heads.
The present invention furthermore relates to an absorbent article, in particular a disposable diaper, comprising a closure tab on each edge portion of the diaper comprising a first mechanical fastening element according to claim 1, said first mechanical fastening element being releasably engagable with a second mechanical fastening on the landing zone of the outside surface of the diaper which is complementary with the first mechanical fastening element, said first mechanical fastening element being adhesively and/or mechanically attachable to other portions of the outside surface of the diaper or to a third mechanical fastening element on the surface of the diaper or on the other closure tab whereby the third mechanical outs) fastening means is complementary with the first mechanical fastening element, said adhesive attachment being obtained by means of the hot-melt pressure-sensitive adhesive (5) present on at least part of the hook heads (3) and/or in at least part of the interstitial spaces (4) between the stems (2) of said first mechanical fastening element and said mechanical attachment being obtained by mechanically engaging the first mechanical fastening element with the outside surface of the diaper or the third mechanical fastening element.
The present invention furthermore relates to a closure tab for an absorbent article, particularly for a disposable diaper, for fastening the article onto the body of a person, said tab comprising a mechanical fastening means according to the invention.